Antenna



Oct. 30, 1951 N. E. LINDENBLAD ANTENNA 3 SheetsSheet 1 Filed Aug. 25, 1945 I ll INVENTOR I/VDfNBL/ID BY #54 ATTORNEY Oct. 30, 1951 N. E. LINDEN BLAD ANTENNA 3 She t-Sheet 2 Filed Aug. 25, 1945 INVENTOR ATTORNEY Oct. 30, 1951 N. E. LINDENYBLAD ANTENNA 3 Sheets-Sheet 5 Filed Aug. 25, 1345 INVENTOR /A/0/V6AD ATTORNEY Patented Oct. 30, 1951 ANTENNA Nils E. Lindenblad, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application August 25, 1945, Serial No. 612,685

- the provision of an antenna, as aforesaid, which is mounted flush with the surface of the vehicle.

Still a further object of the present invention is the provision of an antenna, as aforesaid, which occupies a minimum amount of space in the skin of the vehicle and also a minimum amount of space within the vehicle.

The foregoing objects and others which may appear from the following detailed description are attained by providing in the exterior surface of an aerodynamic vehicle, such as an airplane, a resonant cavity havin one wall et flush with the surface. This Wall has an aper ure therein of such size and shape as to provide a capacitive portion or component which will resonate the rest of the cavity which is inductive. The radiation pattern and the effective radiation resistance of the antenna is obtained from the currents which spread over the skin from the aperture and may be controlled by varying the size and shape of this aperture connecting the interior of the cavity with the exterior of the vehicle. Generally, said aperture will be in the form of an elongated slot having movable capacity flanges along the edges of the slot whereby the tuning of the system may be adjusted. The casing forming the cavity also serves to prevent currents from spreading over invention, it should be clearly understood that the antenna is usable either for the transmission or the reception of radiant energy waves of the operating frequency though, for the sake of avoiding circumlocution, its operation will be described primarily as though used for transmission.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by drawings in which:

Figure 1 illustrates in transverse cross section an embodiment of the present invention, while Figure 2 is a front view in perspective;

Figure 3 is a curve illustrating feature of the operation of the antenna of Figures 1 and 2;

Figure 4 is a transverse cross sectional view illustrating in amplified form a modification of the present invention; while Figures 5 and 6 are transverse and longitudinal cross section views of a further modification of the invention; while Figure 7 illustrates a further modification of the feeding structure shown in Figures 5 and 6.

Referring now to Figures 1 and 2, reference numeral l0 denotes an elongated metallic box havin a front wall 12, a rear wall l5 and a pair of side walls It and H5. The ends of the box are closed by end walls I 1, ll. Front wall I2 is arranged to be mounted flush substantially with the conductive exterior surface of a vehicle by means of a circumferential mounting flange [8. Wall l2 also contains an elongated central slot 20 through which ultra short wave energy escapes from the resonant cavity formed by the box via, the continuity or interlinked currents set up in the sheet and is radiated. Slot -20 is provided at its ends with transverse slots 22 and 24 whereby the end portions of slot 20 are electrically freed one from the other. Therethe operating frequency by adjustment of the capacity loading across slot 20 provided by the condenser plates. Furthermore, the electrical length of the slot may be effectively increased by capacity loading near the ends of the slot. That is, condenser plates 26, 36 and 30, 40 parallel the inductance of the slot at each end and by virtue of approaching resonance permits the building up of higher voltage near the ends of the slot. These condenser plates may be conveniently formed as L-shaped brackets or angle plates ex- .ending inwardly from slot 20 in opposing pairs. io adjust the capacity effect between members of each pair, the base portions of each L-shaped members and the plate 12 upon which they are mounted.

In order to prevent the entrance of dust, moisture, etc. into the resonant cavity HJ, slot is covered with a window 54 of high quality dielec trio material. The window may be made of Lucite which is the trade name of methylmethacrylate or of polystyrene. Since these insulating materials are comparatively soft and under some conditions subject to cold flow, it is not desirable that the window be mounted in position by screws or rivets passing through the insulating material itself into the plate 1.2. In stead, there is provided a bezel member .entirely surrounding the window 44. The bezel is preferably permanently attached to flange it by means of rivets 46 passing through the bezel i5 and the flange 18.

One preferred method of energizing the resonant space within the enclosure 19 is shown in Figure 1. This means of energizing the cavity employs a pair of standard coaxial receptacles 50 and 5| mounted in opposing relationship on opposite walls l4, l6. Each receptacle includes a threaded outer sleeve 52 and an inner jack member 53 adapted to respectively contact the outer sheath and inner conductor of a coaxial trans-- mission line. The outer threaded member 52 is provided with a mounting flange 55 by means of which the receptacles are attached to walls l4 and it. Since the walls l4 and I5 are made of comparatively thin material, stiffening plates 56 may be interposed between the mounting flanges and the side walls I4 and [6. The inner jack members 53 of the coaxial receptacles are mounted in coaxial relationship with the interior of the threaded sleeves 50 by means of high quality insulating material as indicated by reference numeral 51. The inner jack members 53 of coaxial receptacles 50 and 51 are connected together by a large diameter rod 60. Rod 60 is supported by screws 62, 63 passing through jack members 53 into threaded holes in rod 60. It is preferred that the mounting holes for screws 62 and 53 in the ends of rod 60 be set off center to a slight extent. Thus, the effective coupling between the rod 60 and chamber may be varied by rotating the rod. Either of the coaxial recep tacles 5B or 5| may be used as the input terminal for high frequency energy from a transmitter conducted thereto by varied transmissionline TL. The other side has a shorted stub of coaxial transmission line connected thereto such as stub 13. In a particular embodiment actually built and tested a stub of 50 ohm flexible line was used. The stub had an overall length of 34 centimeters when the antenna was operated at a midfrequency of 440 megacycles. At midband frequency the shorted stub line acts as a resonant circuit while the cavity is anti-resonant. Some circuits with particular resistance and reactance varia tions with frequency, exhibit such anti-resonant characteristics. The length of the stub is governed by the anti-resonance characteristic of the .quency range.

cies as abscissae.

antenna so that the stub provides a resonant characteristic of maximum correspondence. The two are effectively connected in series as far as the source of high frequency energy is concerned. A departure from midband frequency may cause, for example, a decrease in impedance of the resonant chamber while it simultaneously causes an increase of impedance of the stub. The total input impedance can in this way be maintained at a substantially constant value over a Wider fre- "Figure 3 illustrates by means of curves the band pass characteristics of the antenna shown in Figures land 2. In Figure 3 standing wave ratios are plotted as ordinates against frequen- The curves H and 12 of Figure '3 illustrate a band pass characteristic for different adjustments of the antenna of Figures 1 and 2. It will be noted that the standing wave ratio for a band of frequencies extending from about 422 megacycles to 4'78 megacycles is at all times less than 1.8and varies over this band less than one tenth.

Figure 4 illustrates a modification of the form of the invention previously discussed with reference to Figures 1 and .2. Similar parts have similar reference characters in all three figures. However, Figure 4 illustrates a different way of tuning the radiating slot 2-D. Herein condenser brackets I5 and I6 carry a pair of opposing round plates or discs 11 and 18. Plate 11 is rigidly fixed to bracket 16 while plate 18 is carried on a threaded rod 19 so that by rotating rod 19, the spacing between plates Ill and 18 may be varied. Figure 4 also illustrates a modified way of feeding the resonant chamber within box ID from the transmitter. The coaxial line fitting 52 .has its inner conductor 53 extended nearly across the width of box It. At the end of extended conduetor 53 is arranged a capacity plate '81 adapted to cooperate with capacity plate 82 connected to the wall I8. Extended conductor 53 is surrounded by an outer sleeve member '80 for almost its full length. By suitably adjusting the spacing between plates 81 and 82, the electrical length or extended conductor 53 may be so varied that resonance is approached, thus varying the coupling of the transmission line connected to conductor 52 to the interior of box 10.

Figures 5 and '6 illustrate a modified feedin arrangement different from that discussed above with reference to Figure 4. Here the inner conductor 53 of the line fitting '52 is connected to the rounded end of tapered tongue 59. Tongue has its broad base edge connected to side wall l6 along its entire length. By suitably adjusting the taper of the curved tongue 90 and its curvature, such coupling distribution is obtained between the chamber inside box l0 and the line connected to cable connector 52 that constant input impedance results over a relatively wide band of frequencies.

Figure 7 illustrates a further modification of the form of the invention shown in Figures 5 and 6 wherein the tongue 98 is U-shaped in cross section. The broad base portion of tongue 92 is electrically connected to the rear wall of box I!) opposite the front wall 12. Tongue 92 has the same curving taper described above with reference to Figures 5 and 6 but it is so bent as to resemble an inverted letter U when viewed from an end of box (6. By varying the taper of the curved tongue 92 and its curvature, similar coupling characteristics are obtained so that substantially constant input impedance obtainsover a relatively wide band of frequencies. The arrangements for tuning slot inFigures 5, 6 and 7 are the same as described above with reference to Figure 4.

While I have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto" since 'many modifications may be made in the several 'plane of a conductive sheet constituting a portion of the body of a vehicle, said front wall having an elongated slot having T-shaped ends therein and means for coupling high frequency energy to the interior of said box including ;a conductive rod passing through said box transversely to said slot, and means-for varying the coupling effect of said rod to the space within said box including means for varying the spacing of said rod with respect to the rear wall of said box, said means including insulated supports for said rod eccentrically located with respect to the axis of said rod and means for rotating said rod.

2. An antenna including a hollow metallic box, the front wall of said box being located in the plane of a conductive sheet constituting a portion of the body of a vehicle, said front wall having an elongated slot having T-shaped ends therein and means for coupling high frequency energy to the interior of said box including a conductive rod passing through saidbox transversely to said slot, and means for varying the coupling effect of said rod to the space within said box including means for varying the spacing of said rod with respect to the rear wall of said box, said means including insulated supports for said rod eccentrically located with respect to the axis of said rod and means for rotating said rod, means for tuning said slot including adjustable angle plates arranged along the edges of said slot in opposing pairs.

3. An antenna system comprising, a conductive sheet having an elongated slot therein, said slot having a dumbbell configuration to increase the effective length thereof, a hollow metallic box fastened on one side of said sheet to enclose said slot, a high frequency energy coupling element comprising a conductive cylinder arranged transversely to said slot within said box, and means to couple high frequency energy to the interior of said box including a first coaxial transmission line having the inner conductor thereof connected to one end of said cylinder and the outer conductor thereof connected to said box, the other end of said first transmission line being coupled to a high frequency transducer, and a second coaxial transmission line having the inner conductor thereof connected to the remaining end of said cylinder and the outer conductor thereof connected to said box, said second transmission line having a length at which the variation in impedance thereof with respect to frequency opposes the variation in impedance of said antenna with respect to the operating frequency.

4. An antenna including a hollow conductive walled box, one wall of said box having an elongated slot therein, and means for coupling high frequency energy to the interior of said box including a conductive rod passing through said box transversely to said slot, and means for varying the coupling effect of said rod to the space withinsaid box, said means including insulated "supports'for saidrod eccentrically located with respect to the-axis of said rod andmeans for rotatingsaidrod. Y v

5.An antenna including a hollow conductive walled box, onewall of said box having an elongated slot therein, means to mount said one wall of said box in the plane of a conductive sheet and means for coupling high'frequency energy to the interior of said box including a coaxial transmission line having a sheath interrupted by the walls of said'box and a center conductor passing through said box transversely to-said slot, and means for varying the coupling effect of said coaxial transmission line to the space within said box including means to mount the portion of said center conductor within said box eccentrically with respect to the axis of said coaxial transmission line and means for rotating said portion about said axis.

' 6.-An antenna including a hollow conductive walled box, one wall of said box having an elongated slot therein, means to mount said one wall of saidbox in'the plane of a conductive sheet and means for coupling high frequency energy to the interior of said box including a pair of coaxial transmission line sections having sheath conductors connected in registry with respect to each other to opposite walls of said box and center conductors connected in series relationship by a conductive rod passing through said box transversely to said slot, and means for varying the coupling effect of said coaxial transmission line to the space within saidbox including means to mount said conductive rod eccentrically with respect to the axis of said coaxial transmission line section, means for rotating said rod about said axis, one of said transmission line sections having a length at which the variation of impedance with frequency variation is equal and opposite to the variation of said antenna, and means to couple transducer apparatus to the other transmission line section.

'7. An antenna including a hollow conductive walled box, one wall of said box having an elongated slot therein, means to mount said one wall of said box in the plane of a conductive sheet and means for coupling high frequency energy to the interior of said box including a pair of coxaial transmission line sections having sheath conductors connected in registry with respect to each other to opposite walls of said box and center conductors connected in series relationship by a conductive rod passing through said box transversely to said slot, and means for varying the coupling effect of said coaxial transmission line to the space within said box including means to mount said conductive rod eccentrically with respect to the axis of said coaxial transmission line sections, means for rotating said rod about said axis, one of said transmission line sections being short circuited and having a length at which the variation of impedance with frequency variation is equal and opposite to the variation of said antenna, and means to couple transducer apparatus to the other transmission line section. 8. An antenna including a hollow metallic box, the front wall of said box being located in the plane of a conductive sheet, said front Wall having an elongated slot therein, and means for coupling high frequency energy to the interior of said box including a conductive rod passing through said box, transverse to said slot, and means for varying the coupling effect of said rod to the space within said box including insulated '37 supp rts for said rod eccentri -an located with respect to the axis of said rod and means for rotating said rod and means for tuning said slot, including angle plates in opposing pairs and being individually adjustable along the edges ,of said slot.

9. An antenna including a hollow metallic box, the front wall of said box being located in the plane of a conductive sheet constituting a portion of .the body of .a vehicle, said front wall having an elongated slot having T-shaped ends therein,

vand means for coupling high frequency energy .to

the interior of said .box including a conductive rod passing through said box transversely to said slot, and means for varying the coupling efiect of said rod to the space within said box including insulated supports ,for said rod eccentrically located with respect to the axis of said rod and means for rotating said rod, means for tuning said slot including capacity plates arranged-along the edges of said .slot in cooperating pairs, the :plates of each of said pairs :being adjustable with respect to each other.

NILS ,E. LINDENBLAD.

nsrsannces QITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,206,923 .Southworth 1, July 9, 1940 2,238,770 Blumlein Apr. 15, 1941 2,258,953 Higgins Oct. 14, 1941 2,284,434 Lindenblad ,May26, 1942 2,407,068 Fiske et al. -,,1 Sept. 3, 1946 2,415,807 Barrow et ,al. Feb. 18, 1947 2,425,303 Carter Aug. '12, 1947 2,431,124 Kees .et a1. Nov. 18, 1947 2,433,368 Johnson et al. Dec. .30, 1947 2,435,988 Varian Feb. 17, 1948 FOREIGN PATENTS Number Country Date 604,353 Germany Jan. 15, 1933 841,036 France May 9, 1939 

